With the development and deployment of mobile devices such as laptop computers, personal digital assistant devices, cell phones, etc. and infrastructures, consumers and businesses are increasingly being able to realize the benefits of true mobile computing, collaboration, and information exchange. No longer are business travelers required to carry an assortment of cables and search endlessly for an available data port simply to connect to a network to retrieve email messages, download files, or exchange information. No longer are companies and home consumers restrained in where they may access their networks by the location of the Ethernet jacks on the wall. Meeting participants and groups of friends may now form their own ad hoc networks without connecting cables between themselves or logging in to some preexisting network. They can log onto the network using a wireless protocol while running on battery power, thereby allowing even greater mobility.
Hand-in-hand with mobile devices, electronic messaging such as electronic mail (“e-mail”) and instant messaging carried over the Internet, is rapidly becoming not only quite pervasive in society but also, given its informality, ease of use and low cost, a preferred method of communication for many individuals and organizations. However, electronic messaging requires the users of the mobile devices to be within the range of the wireless networks they are on or subscribe to in order to receive messages. When users come back in the network after being out of range or when first logging in, the users often want to know if there are any messages waiting. Additionally, many users want to be notified when an event of interest occurs such as a particular message arriving, news of an event (e.g., calendar update), etc. so that the users can connect with the server of the network and retrieve the message/event/etc.
The most straightforward way to ensure that a user is kept in sync with a server is to send a sync notification (e.g., a ping) to the client whenever an event of interest occurs on the server. The client then connects back to the server to retrieve the data. This methodology requires a large number of notifications, which in turn consumes additional server CPU cycles, network bandwidth and battery life on the client. In today's network environments where users of a network are charged based upon time of day, length of time, and/or bandwidth usage, the notifications can increase the cost for the user. For example, where notifications are delivered over SMS (Short Messaging Service), this approach can significantly increase a user's monthly bill and waste carrier resources.
Industry has taken some steps to mitigate the cost of notifications. Some mitigations include waiting for a certain amount of time to elapse or a certain number of items to accumulate before sending the notification. However, all such approaches introduce latency into the system that does not have to be there. These approaches make a user wait five to ten minutes or longer for their email when the user can get it right away.